Variable impedance devices are used in a variety of applications. For example, they can be used in RF instrumentation, to test certain devices such as transistors under a range of load conditions, and thereby provide device characterization.
Such variable impedance devices are generally off-chip devices having a passive tuner network comprising components such as variable capacitors, variable inductors and variable resistors in order to provide variable impedance.
Certain applications such as 60 GHz WLAN (wireless local area networks), wireless HDMI (high definition multimedia interface), wireless USB (universal serial bus) and 77 GHz automotive radars require active devices capable of high performance at relatively high frequencies of 60 GHz or over.
However, a drawback of existing variable impedance devices is that they tend to be relatively costly and/or they are not adapted to such high frequency ranges.